AsyncTask as kotlin coroutine

To use a coroutine you need a couple of things:

• Implement CoroutineScope interface.
• References to Job and CoroutineContext instances.
• Use suspend function modifier to suspend a coroutine without blocking the Main Thread when calling function that runs code in Background Thread.
• Use withContext(Dispatchers.IO) function to run code in background thread and launch function to start a coroutine.

Usually I use a separate class for that, e.g. “Presenter” or “ViewModel”:

class Presenter : CoroutineScope {
    private var job: Job = Job()
    override val coroutineContext: CoroutineContext
        get() = Dispatchers.Main + job // to run code in Main(UI) Thread

    // call this method to cancel a coroutine when you don't need it anymore,
    // e.g. when user closes the screen
    fun cancel() {
        job.cancel()
    }

    fun execute() = launch {
        onPreExecute()
        val result = doInBackground() // runs in background thread without blocking the Main Thread
        onPostExecute(result)
    }

    private suspend fun doInBackground(): String = withContext(Dispatchers.IO) { // to run code in Background Thread
        // do async work
        delay(1000) // simulate async work
        return@withContext "SomeResult"
    }

    // Runs on the Main(UI) Thread
    private fun onPreExecute() {
        // show progress
    }

    // Runs on the Main(UI) Thread
    private fun onPostExecute(result: String) {
        // hide progress
    }
}

With ViewModel the code is more concise using viewModelScope:

class MyViewModel : ViewModel() {
    
    fun execute() = viewModelScope.launch {
        onPreExecute()
        val result = doInBackground() // runs in background thread without blocking the Main Thread
        onPostExecute(result)
    }

    private suspend fun doInBackground(): String = withContext(Dispatchers.IO) { // to run code in Background Thread
        // do async work
        delay(1000) // simulate async work
        return@withContext "SomeResult"
    }

    // Runs on the Main(UI) Thread
    private fun onPreExecute() {
        // show progress
    }

    // Runs on the Main(UI) Thread
    private fun onPostExecute(result: String) {
        // hide progress
    }
}

To use viewModelScope add next line to dependencies of the app’s build.gradle file:

implementation "androidx.lifecycle:lifecycle-viewmodel-ktx:$LIFECYCLE_VERSION"

At the time of writing final LIFECYCLE_VERSION = "2.3.0-alpha04"

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Here is also implementation of Async Task using Kotlin coroutines and extension function on CoroutineScope.